sea holly vs shrub

sea holly and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea holly	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of sea holly; that is, shrub is a word with a broader meaning than sea holly:

sea holly: European evergreen eryngo with twisted spiny leaves naturalized on United States east coast; roots formerly used as an aphrodisiac
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of sea holly include bush.

sea holly (noun)	shrub (noun)
European evergreen eryngo with twisted spiny leaves naturalized on United States east coast; roots formerly used as an aphrodisiac	a low woody perennial plant usually having several major stems
widely cultivated southern European acanthus with whitish purple-veined flowers